1. Field of the Invention
The present invention relates to a vibrating sensor, e.g. suitable for use in constituting a gyro.
2. Brief Discussion of the Prior Art
Vibrating gyros are known that comprise a base and a resonator secured to the base. The base and the resonator are associated with electrodes that are organized in two groups that are connected in alternation to a detection and control circuit via a first connection channel and then a second connection channel, with each of the groups of electrodes being connected to a respective one of the channels.
The control circuit comprises excitation electronics and detection electronics and is arranged to control an excitation stage and a detection stage on each of the connection channels, the excitation stages and the detection stages having substantially identical respective durations (e.g. 60 microseconds (μs) for the excitation stages and 140 μs for the detection stages). The durations of the detection and excitation stages may vary as a function of the sensor in question. The control circuit is generally arranged to perform the following sequence: excitation stage on the first connection channel; excitation stage on the second connection channel; detection stage on the first connection channel; detection stage on the second connection channel.
That sequencing makes it possible to use the same excitation electronics for exciting both groups of electrodes, and the same detection electronics for detecting signals provided by both groups of electrodes. This serves to limit the influence of differences in gain and phase on the two channels, which differences might give rise to a setting angle error and to drift of the gyro. Nevertheless, that sequencing causes couplings to appear between the various stages. Those couplings are associated, for example, with memory effects in the digital-to-analog converters that result from stray capacitances of the printed circuit card on which the circuits are formed, which capacitances, in series with high value resistances present in the electronics, give rise to disturbances over a length of time that may be greater than the duration of a stage. Couplings may occur between two successive detection stages, two successive excitation stages, a detection stage and an excitation stage following said detection stage, or an excitation stage and a detection stage following said excitation stage. Coupling gives rise to bias in the following stage, which bias is proportional to the control signal processed during the preceding stage. These last two couplings, due in particular to charge accumulating on the electrodes, provide the majority contribution to the mean drift of the gyro, and it is difficult to limit this drift by electronic compensation.
The instability of those defects has a strong influence on the performance of the sensor, particularly in a humid environment.
Proposals have been made to reduce the control or precession dynamic range in order to remedy the above-mentioned drawbacks. Proposals have been made to introduce additional relaxation times in order to limit those defects.